5 Within the check phase of type check, we check each item one at a time
6 (bodies of function expressions are checked as part of the containing
7 function). Inference is used to supply types wherever they are unknown.
9 By far the most complex case is checking the body of a function. This
10 can be broken down into several distinct phases:
12 - gather: creates type variables to represent the type of each local
13 variable and pattern binding.
15 - main: the main pass does the lion's share of the work: it
16 determines the types of all expressions, resolves
17 methods, checks for most invalid conditions, and so forth. In
18 some cases, where a type is unknown, it may create a type or region
19 variable and use that as the type of an expression.
21 In the process of checking, various constraints will be placed on
22 these type variables through the subtyping relationships requested
23 through the `demand` module. The `infer` module is in charge
24 of resolving those constraints.
26 - regionck: after main is complete, the regionck pass goes over all
27 types looking for regions and making sure that they did not escape
28 into places where they are not in scope. This may also influence the
29 final assignments of the various region variables if there is some
32 - writeback: writes the final types within a function body, replacing
33 type variables with their final inferred types. These final types
34 are written into the `tcx.node_types` table, which should *never* contain
35 any reference to a type variable.
39 While type checking a function, the intermediate types for the
40 expressions, blocks, and so forth contained within the function are
41 stored in `fcx.node_types` and `fcx.node_substs`. These types
42 may contain unresolved type variables. After type checking is
43 complete, the functions in the writeback module are used to take the
44 types from this table, resolve them, and then write them into their
45 permanent home in the type context `tcx`.
47 This means that during inferencing you should use `fcx.write_ty()`
48 and `fcx.expr_ty()` / `fcx.node_ty()` to write/obtain the types of
49 nodes within the function.
51 The types of top-level items, which never contain unbound type
52 variables, are stored directly into the `tcx` typeck_results.
54 N.B., a type variable is not the same thing as a type parameter. A
55 type variable is an instance of a type parameter. That is,
56 given a generic function `fn foo<T>(t: T)`, while checking the
57 function `foo`, the type `ty_param(0)` refers to the type `T`, which
58 is treated in abstract. However, when `foo()` is called, `T` will be
59 substituted for a fresh type variable `N`. This variable will
60 eventually be resolved to some concrete type (which might itself be
66 mod compare_impl_item;
73 pub use check::check_abi;
75 use check::check_mod_item_types;
76 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
77 use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
79 use rustc_hir::def_id::{DefId, LocalDefId};
80 use rustc_hir::intravisit::Visitor;
81 use rustc_index::bit_set::BitSet;
82 use rustc_middle::ty::query::Providers;
83 use rustc_middle::ty::{self, Ty, TyCtxt};
84 use rustc_middle::ty::{InternalSubsts, SubstsRef};
85 use rustc_session::parse::feature_err;
86 use rustc_span::source_map::DUMMY_SP;
87 use rustc_span::symbol::{kw, Ident};
88 use rustc_span::{self, BytePos, Span, Symbol};
89 use rustc_target::abi::VariantIdx;
90 use rustc_target::spec::abi::Abi;
91 use rustc_trait_selection::traits::error_reporting::suggestions::ReturnsVisitor;
92 use std::num::NonZeroU32;
94 use crate::require_c_abi_if_c_variadic;
95 use crate::util::common::indenter;
97 use self::compare_impl_item::collect_return_position_impl_trait_in_trait_tys;
98 use self::region::region_scope_tree;
100 pub fn provide(providers: &mut Providers) {
101 wfcheck::provide(providers);
102 *providers = Providers {
104 check_mod_item_types,
106 collect_return_position_impl_trait_in_trait_tys,
107 compare_impl_const: compare_impl_item::compare_impl_const_raw,
112 fn adt_destructor(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::Destructor> {
113 tcx.calculate_dtor(def_id, dropck::check_drop_impl)
116 /// Given a `DefId` for an opaque type in return position, find its parent item's return
118 fn get_owner_return_paths(
121 ) -> Option<(LocalDefId, ReturnsVisitor<'_>)> {
122 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
123 let parent_id = tcx.hir().get_parent_item(hir_id).def_id;
124 tcx.hir().find_by_def_id(parent_id).and_then(|node| node.body_id()).map(|body_id| {
125 let body = tcx.hir().body(body_id);
126 let mut visitor = ReturnsVisitor::default();
127 visitor.visit_body(body);
132 /// Forbid defining intrinsics in Rust code,
133 /// as they must always be defined by the compiler.
134 // FIXME: Move this to a more appropriate place.
135 pub fn fn_maybe_err(tcx: TyCtxt<'_>, sp: Span, abi: Abi) {
136 if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
137 tcx.sess.span_err(sp, "intrinsic must be in `extern \"rust-intrinsic\" { ... }` block");
141 fn maybe_check_static_with_link_section(tcx: TyCtxt<'_>, id: LocalDefId) {
142 // Only restricted on wasm target for now
143 if !tcx.sess.target.is_like_wasm {
147 // If `#[link_section]` is missing, then nothing to verify
148 let attrs = tcx.codegen_fn_attrs(id);
149 if attrs.link_section.is_none() {
153 // For the wasm32 target statics with `#[link_section]` are placed into custom
154 // sections of the final output file, but this isn't link custom sections of
155 // other executable formats. Namely we can only embed a list of bytes,
156 // nothing with provenance (pointers to anything else). If any provenance
157 // show up, reject it here.
158 // `#[link_section]` may contain arbitrary, or even undefined bytes, but it is
159 // the consumer's responsibility to ensure all bytes that have been read
160 // have defined values.
161 if let Ok(alloc) = tcx.eval_static_initializer(id.to_def_id())
162 && alloc.inner().provenance().ptrs().len() != 0
164 let msg = "statics with a custom `#[link_section]` must be a \
165 simple list of bytes on the wasm target with no \
166 extra levels of indirection such as references";
167 tcx.sess.span_err(tcx.def_span(id), msg);
171 fn report_forbidden_specialization(
173 impl_item: &hir::ImplItemRef,
176 let mut err = struct_span_err!(
180 "`{}` specializes an item from a parent `impl`, but \
181 that item is not marked `default`",
184 err.span_label(impl_item.span, format!("cannot specialize default item `{}`", impl_item.ident));
186 match tcx.span_of_impl(parent_impl) {
188 err.span_label(span, "parent `impl` is here");
190 "to specialize, `{}` in the parent `impl` must be marked `default`",
195 err.note(&format!("parent implementation is in crate `{cname}`"));
202 fn missing_items_err(
205 missing_items: &[&ty::AssocItem],
206 full_impl_span: Span,
208 let missing_items_msg = missing_items
210 .map(|trait_item| trait_item.name.to_string())
214 let mut err = struct_span_err!(
218 "not all trait items implemented, missing: `{missing_items_msg}`",
220 err.span_label(impl_span, format!("missing `{missing_items_msg}` in implementation"));
222 // `Span` before impl block closing brace.
223 let hi = full_impl_span.hi() - BytePos(1);
224 // Point at the place right before the closing brace of the relevant `impl` to suggest
225 // adding the associated item at the end of its body.
226 let sugg_sp = full_impl_span.with_lo(hi).with_hi(hi);
227 // Obtain the level of indentation ending in `sugg_sp`.
229 tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());
231 for trait_item in missing_items {
232 let snippet = suggestion_signature(trait_item, tcx);
233 let code = format!("{}{}\n{}", padding, snippet, padding);
234 let msg = format!("implement the missing item: `{snippet}`");
235 let appl = Applicability::HasPlaceholders;
236 if let Some(span) = tcx.hir().span_if_local(trait_item.def_id) {
237 err.span_label(span, format!("`{}` from trait", trait_item.name));
238 err.tool_only_span_suggestion(sugg_sp, &msg, code, appl);
240 err.span_suggestion_hidden(sugg_sp, &msg, code, appl);
246 fn missing_items_must_implement_one_of_err(
249 missing_items: &[Ident],
250 annotation_span: Option<Span>,
252 let missing_items_msg =
253 missing_items.iter().map(Ident::to_string).collect::<Vec<_>>().join("`, `");
255 let mut err = struct_span_err!(
259 "not all trait items implemented, missing one of: `{missing_items_msg}`",
261 err.span_label(impl_span, format!("missing one of `{missing_items_msg}` in implementation"));
263 if let Some(annotation_span) = annotation_span {
264 err.span_note(annotation_span, "required because of this annotation");
270 fn default_body_is_unstable(
275 reason: Option<Symbol>,
276 issue: Option<NonZeroU32>,
278 let missing_item_name = &tcx.associated_item(item_did).name;
279 let use_of_unstable_library_feature_note = match reason {
280 Some(r) => format!("use of unstable library feature '{feature}': {r}"),
281 None => format!("use of unstable library feature '{feature}'"),
284 let mut err = struct_span_err!(
288 "not all trait items implemented, missing: `{missing_item_name}`",
290 err.note(format!("default implementation of `{missing_item_name}` is unstable"));
291 err.note(use_of_unstable_library_feature_note);
292 rustc_session::parse::add_feature_diagnostics_for_issue(
294 &tcx.sess.parse_sess,
296 rustc_feature::GateIssue::Library(issue),
301 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
302 fn bounds_from_generic_predicates<'tcx>(
304 predicates: ty::GenericPredicates<'tcx>,
305 ) -> (String, String) {
306 let mut types: FxHashMap<Ty<'tcx>, Vec<DefId>> = FxHashMap::default();
307 let mut projections = vec![];
308 for (predicate, _) in predicates.predicates {
309 debug!("predicate {:?}", predicate);
310 let bound_predicate = predicate.kind();
311 match bound_predicate.skip_binder() {
312 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
313 let entry = types.entry(trait_predicate.self_ty()).or_default();
314 let def_id = trait_predicate.def_id();
315 if Some(def_id) != tcx.lang_items().sized_trait() {
316 // Type params are `Sized` by default, do not add that restriction to the list
317 // if it is a positive requirement.
318 entry.push(trait_predicate.def_id());
321 ty::PredicateKind::Clause(ty::Clause::Projection(projection_pred)) => {
322 projections.push(bound_predicate.rebind(projection_pred));
327 let generics = if types.is_empty() {
334 .filter_map(|t| match t.kind() {
335 ty::Param(_) => Some(t.to_string()),
336 // Avoid suggesting the following:
337 // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
344 let mut where_clauses = vec![];
345 for (ty, bounds) in types {
347 .extend(bounds.into_iter().map(|bound| format!("{}: {}", ty, tcx.def_path_str(bound))));
349 for projection in &projections {
350 let p = projection.skip_binder();
351 // FIXME: this is not currently supported syntax, we should be looking at the `types` and
352 // insert the associated types where they correspond, but for now let's be "lazy" and
353 // propose this instead of the following valid resugaring:
354 // `T: Trait, Trait::Assoc = K` → `T: Trait<Assoc = K>`
355 where_clauses.push(format!("{} = {}", tcx.def_path_str(p.projection_ty.def_id), p.term));
357 let where_clauses = if where_clauses.is_empty() {
360 format!(" where {}", where_clauses.join(", "))
362 (generics, where_clauses)
365 /// Return placeholder code for the given function.
366 fn fn_sig_suggestion<'tcx>(
368 sig: ty::FnSig<'tcx>,
370 predicates: ty::GenericPredicates<'tcx>,
371 assoc: &ty::AssocItem,
378 Some(match ty.kind() {
379 ty::Param(_) if assoc.fn_has_self_parameter && i == 0 => "self".to_string(),
380 ty::Ref(reg, ref_ty, mutability) if i == 0 => {
381 let reg = format!("{reg} ");
382 let reg = match ®[..] {
386 if assoc.fn_has_self_parameter {
387 match ref_ty.kind() {
388 ty::Param(param) if param.name == kw::SelfUpper => {
389 format!("&{}{}self", reg, mutability.prefix_str())
392 _ => format!("self: {ty}"),
399 if assoc.fn_has_self_parameter && i == 0 {
400 format!("self: {ty}")
407 .chain(std::iter::once(if sig.c_variadic { Some("...".to_string()) } else { None }))
409 .collect::<Vec<String>>()
411 let output = sig.output();
412 let output = if !output.is_unit() { format!(" -> {output}") } else { String::new() };
414 let unsafety = sig.unsafety.prefix_str();
415 let (generics, where_clauses) = bounds_from_generic_predicates(tcx, predicates);
417 // FIXME: this is not entirely correct, as the lifetimes from borrowed params will
418 // not be present in the `fn` definition, not will we account for renamed
419 // lifetimes between the `impl` and the `trait`, but this should be good enough to
420 // fill in a significant portion of the missing code, and other subsequent
421 // suggestions can help the user fix the code.
422 format!("{unsafety}fn {ident}{generics}({args}){output}{where_clauses} {{ todo!() }}")
425 pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
426 Some(match ty.kind() {
429 ty::Int(_) | ty::Uint(_) => "42",
430 ty::Float(_) => "3.14159",
431 ty::Error(_) | ty::Never => return None,
436 /// Return placeholder code for the given associated item.
437 /// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
438 /// structured suggestion.
439 fn suggestion_signature(assoc: &ty::AssocItem, tcx: TyCtxt<'_>) -> String {
441 ty::AssocKind::Fn => {
442 // We skip the binder here because the binder would deanonymize all
443 // late-bound regions, and we don't want method signatures to show up
444 // `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound
445 // regions just fine, showing `fn(&MyType)`.
448 tcx.fn_sig(assoc.def_id).skip_binder(),
450 tcx.predicates_of(assoc.def_id),
454 ty::AssocKind::Type => format!("type {} = Type;", assoc.name),
455 ty::AssocKind::Const => {
456 let ty = tcx.type_of(assoc.def_id);
457 let val = ty_kind_suggestion(ty).unwrap_or("value");
458 format!("const {}: {} = {};", assoc.name, ty, val)
463 /// Emit an error when encountering two or more variants in a transparent enum.
464 fn bad_variant_count<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>, sp: Span, did: DefId) {
465 let variant_spans: Vec<_> = adt
468 .map(|variant| tcx.hir().span_if_local(variant.def_id).unwrap())
470 let msg = format!("needs exactly one variant, but has {}", adt.variants().len(),);
471 let mut err = struct_span_err!(tcx.sess, sp, E0731, "transparent enum {msg}");
472 err.span_label(sp, &msg);
473 if let [start @ .., end] = &*variant_spans {
474 for variant_span in start {
475 err.span_label(*variant_span, "");
477 err.span_label(*end, &format!("too many variants in `{}`", tcx.def_path_str(did)));
482 /// Emit an error when encountering two or more non-zero-sized fields in a transparent
484 fn bad_non_zero_sized_fields<'tcx>(
486 adt: ty::AdtDef<'tcx>,
488 field_spans: impl Iterator<Item = Span>,
491 let msg = format!("needs at most one non-zero-sized field, but has {field_count}");
492 let mut err = struct_span_err!(
496 "{}transparent {} {}",
497 if adt.is_enum() { "the variant of a " } else { "" },
501 err.span_label(sp, &msg);
502 for sp in field_spans {
503 err.span_label(sp, "this field is non-zero-sized");
508 // FIXME: Consider moving this method to a more fitting place.
509 pub fn potentially_plural_count(count: usize, word: &str) -> String {
510 format!("{} {}{}", count, word, pluralize!(count))